When Towing The TM Which Regulator Controls Battery Charging?

[Philip]

Hello Folks,

I am considering upgrading my batteries on my 2008, 2720 TM since I plan to do a lot of dry camping. The problem is that any really good deep cycle battery, either Gell or AGM, requires a fairly precise charging procedure. The required procedure calls for a three step charging regimen(bulk, absorbtion and float) all with fairly precise voltage levels. Fortunately, my TM came with a three step charger which is used when plugged into 110V AC. This regulation may be adequate for an AGM battery but unfortunately will not meet a Gell batteries charging requirements. I have extensive experience with Gell batteries and am convinced they are more durable and less maintenance than AGM's but alas they need a special regulator. AGM's are still a vast improvement over other deep cycle batteries and they may be able to live with my TM regulator so I will have to go with them.

I know I am going on too long here but I need to know if while towing the TM does the TV alternator use it's internal regulator to charge the TM batteries or does the TV alternator output get regulated by the TM regulator?

If the TV alternator regulator controls charging I will not be able to use the AGM batteries since an automobile regulator is not acceptable. Yes I could install a proper external regulator on my TV but this is a costly project with many complications that I am not sure I want to get involved with. My TV is a 2005 Toyota 4Runner, V8 with a factory tow package(which comes with an upgraded alternator).

Any help would be appreciated,

Phil Friess

[ZekenSpider]

This is my experience with my new TM 3326. The TV is a 2004 Suburban with a 10 gauge wire to the TM tow receptacle. It has 30 Amp fuses at both the TV and TM battery buss end. As I get ready to tow, I set the refrigerator to 12 Volts DC (and refrig. fan on) with shore power still on. Then I connect the TV with engine running. The TV voltmeter sits at 14.7 volts. The TM battery voltage is 14.6. I disconnect shore power and see no change. The TV voltmeter stays at 14.7 volts for the length of the tow (so far, only 200 miles) and the TM battery remains at 14.6 volts whenever I stop, as long as the TV generator is running.

Unless you have a battery isolator (to isolate your TM from your TV) the two batteries (the TM and the TV) will be in parallel and will receive the same charging voltage from the TV generator. That voltage will be controlled by the TV generator regulator which is set to around 14.7 volts. The TV generator will jamb as much current into each battery as they each will accept based on their individual internal voltage levels and the voltage drop encountered in the wire length and size of each charging circuit. The maximum current into the TM battery will be limited by the TV or TM battery circuit fuse (or circuit breaker).

In practice, this means the TV generator(while running) will be a constant source of DC current at 14.7 volts into the TM DC buss. That buss will be providing continual current to your TM equipment (usually just the refrigerator) and to the TM battery up to the limit of the fuses. That will force the TM battery internal voltage to rise to 14.7 volts.

By the same analysis, when on shore power, the TM and TV battery will be charged by the TM inverter (if the TM and TV are still plugged into each other and the TV is not running). In addition, if you have a solar power system on the TM, the solar power regulator will charge the TM battery at a fixed 14.3 (adjustable) voltage.

The TM battery voltage always rises to the solar regulator set point. The only time I see the TM inverter 3 level control come into play is when parked in storage at night with no loads turned on.

I have wondered about using AGM batteries. Let me know if you think they will be durable. So far, in my application, I do not go very far into discharge cycle.

Jerry Miller

[Bill]

Jerry's synopsis is pretty good. Let me add a couple minor things. First, as Jerry said, when towing, the tow vehicle's regulator controls the voltage that is produced at the regulator. The voltage seen at the TM battery will always be lower, due to the voltage drop encountered in the wires running from the tow vehicle regulator to the TM battery and back. This can be several tenths of a volt, depending on the details of the wiring, and the amount of current being drawn through those wires. If the refrigerator is running on DC while you tow, it draws quite a bit of current, and so the charge voltage available to the TM battery will be considerably lower than the voltage seen at the tow vehicle regulator. In fact, for about 1 in 5 of us, the charge voltage drops so low with the refrigerator running that the TM battery actually begins to discharge while we drive. Four chances out of five say you won't be in that group, but nonetheless, the lowered voltage from the tow vehicle can't overcharge your TM battery.

As a second point, the 3-stage regimen for charging batteries (any battery, not just AGM or gel) usually takes a fairly long time to complete, even if full charge current is available from the source. And that's a big IF. Considering the reduced charge current available from the tow vehicle (even if the refrigerator is off), the whole cycle could take days to complete. In the few hours that you are driving, the cycle wouldn't complete, so you certainly don't have to worry about over-charging (which I gather is your concern).

Finally, as Jerry says, when you are plugged into shore power, the TM's charger will determine the charge voltage that is available to the TM battery. Many standalone chargers have a gel setting, but I'm not at all sure that the charger in a 2008 TM has one. Wish I had a manual - perhaps when you get your TM, you could forward the converter's model number to me and I'll look it up. Your choices would seem to be to a) charge the battery correctly at home, with the entire 3-stage regimen at the prescribed voltages, and let the battery take what it can get when you're camping with shore power, or b) replace the TM's charger with one specifically designed for your battery. In my opinion, this would be gross overkill, given that the TM's charger is already a 3-stage charger - but that's just my opinion.

Flooded (conventional) batteries, AGM, and gel batteries are all lead-acid batteries, and use the same chemistry. Both AGM and gel cells are sealed, so overcharging must be carefully controlled since any water lost to gasification cannot easily be replaced. But AGM batteries seem to be superior to gel cells, since AGMs use the same charging voltages as automotive batteries. They are considered a drop-in replacement for flooded batteries in deep-cycle applications. Gel cells, on the other hand, need a slightly lower charge voltage, as you mentioned.

To summarize, web sources say that you're OK for sure with an AGM. I think you are OK with a gel as well, because of the limited charge current available. When you have a choice, though, the sources I find say that an AGM is preferable because no special charge parameters are needed.

Further reading from a reputable battery supplier - http://www.windsun.com/Batteries/Battery_FAQ.htm

Bill

I have extensive experience with Gell batteries and am convinced they are more durable and less maintenance than AGM's but alas they need a special regulator.


On a side note to this post, I do not understand the above statement. As I have never had a Gel battery I cannot speak to that. I CAN attest to the reliability of a AGM battery, also its ability to be maintenance free (at least the one I have, a Lifeline AGM). I have had this battery for over 3 years, and I have done nothing, absolutely nothing to it. During the winter it was stored in the garage, where the temperature regularly got into the teens and twenties. Each spring when I took it out and put it in the TM I didn't even have to recharge it. I couldn't be happier with this battery, especially having to deal with water, charging etc. with the original battery. A whole lot more expensive that a regular deep cycle battery, but to ME it is worth every penny.

Mike Anderson

I am rather perplexed about the advantages of gel or agm over flooded batteries.

I have a pair of Interstate group 24 RV/marine batteries

We have had hookups 4 times since 2005.

We camp about 6 times a year, for not more than a week.

I have added water to the batteries once.

My batteries have been in use since March 2005, a little over 4 years.

Of all of my concerns about preventative maintenance around the house, trucks, cars, motorcycles, ATVs, pool, etc. the TM batteries are at the bottom of the list.

I guess if I was full timing then I would have a different experience. But for weekend camping flooded cells seem to be problem and maintenance free.

Am I just lucky?

Well Wayne....I guess I was unlucky. On my old Aliner with a Interstate battery, I was constantly charging it and adding water. Now mind you I have a good battery charger A Xantrex 10 (or some such number), which does the 3 stages of charging you and many others recommend. I got sick and tired of every time I wanted to go anywhere I had to mess with that battery. Not the least of which having to keep distilled water available. It is possible it was defective (although it did work when I had it charged), but that experience soured me, such that I was willing to pay a LOT more for the Lifeline battery I eventually bought. Obviously, you (and many others) have had excellent luck with regular RV batteries and that is great. For me I will not go back.

Mike

Just a guess, your Aliner may not have had a 3 stage converter.

My TM has a 3 stage charger, but it is not the top of the line either.

I have never seen any evidence that the water has boiled in my batteries. It sounds like you had an over charging problem.

[Wavery]

I lived on my yacht for 14 years and depended on 3 banks of batteries and have used every configuration known to man (including series of industrial 2V batteries @ 200# each).

I agree that gel-cell batteries are the way to go for RV use. I have had extensive experience (4 years @ 365 days a year usage) with gel-cells and found them far superior in charging, discharging and ease of maintenance. However, like anything else, there is a down side as the OP poster alluded too.

Gel-cells do not have the cooling capability of "Water" type batteries. Water dissipates heat much better. Therefore, it is critical that a gel-cell battery never sees anything over 14.4V (thus the special charger). If it does see over 14.4V the case of the battery will literally melt and the sides will cave in. I used to see this all the time on charter fishing boats that change over to gel-cells and run their engines all day long, putting out 14.8V.

Most automotive alternators have a maximum voltage adjustment screw on the alternator case somewhere. Just find out where yours is, and turn the max V down to about 14.5 or 14.6. Your trailer batteries will never see over 14.4.

The next time I buy batteries for our TM, it will be 2 - 4D gel cells. They're pretty heavy but they can be mounted standing on end, if I want.

Originally Posted by harveyrv

The next time I buy batteries for our TM, it will be 2 - 4D gel cells. They're pretty heavy but they can be mounted standing on end, if I want.

I wish I could do something like that.

Because my batteries are on the tongue and I have the swing tongue, anything taller than my group 24 batteries does not fit. I can't use the popular Trojan T105s for that reason.

I can go longer, to a pair of group 27s. A pair of group 31s would be too long. And anything wider will not fit in the tray.

I have very few options in terms of size.

Very good info, though.

[Philip]

To Jerry Miller & Bill,

Thank you for educating me on the workings of the TV & TM charging regulators. From this it appears that I will not be able to use Gell Batteries without extensive changes to the charging systems which I feel are not worth the effort/expense. I am going to continue to investigate the possibility of using AGM batteries with little or no system changes.

The three stage charging regulator supplied with the TM is a WFCO unit. I plan to talk to them and get the voltage points for the three charging stages. I don't have much hope that the voltage points are adjustable for different battery types but I will find out. Perhaps the existing setpoints are reasonably accceptable for AGM batteries and will not affect battery life too much. If the TM charger proves acceptable my only concern will be the bulk charging voltage for the TV regulator. It may not be too harmfull if the battery is in the Bulk or even Absorption phase of charging but I would assume that it would be harmful if the battery was in the Float phase. Perhaps the battery would rarely reach the Float phase with the relatively short times, compared to what is normally required to reach float on a larger capacity battery, you are towing the TM. I will have to make a judgment on that.

I am interested in a high capacity/high quality deep cycle battery since I will be living in the TM for extended periods(three or more months at a time) and plan to dry camp a fair portion of this time. I want the reduced maintenance and durability/long term capcity of a high quality battery. However, I don't want to waste the battery due to a poor charging regimen. These batteries are expensive.

In any event I will at the very least have to get a battery monitor that keeps accurate tabs on amps in/out of the battery to keep tabs on battery charge level. It is not possible to know charge level from battery voltage unless you let the battery rest something like 24 hours or more with no load or charge. This is a luxuary I will never have so I must get a good battery monitor - at the least!!

Thank you again for the help,

Phil Friess